1. Field of the Invention
This invention relates to a circuit system to interconnect semiconductor module carriers, each having a plurality of semiconductor chips, by means of a flexible printed circuit carrier having contact pads which match corresponding contact pads on the module carrier.
2. Description of the Prior Art
As semiconductor processing techniques are improved, chips of ever increasing density can be produced. Semiconductor modules have improved from two or three pin packaging used for diodes and transistors to four, eight and sixteen pin flat packs and the larger 200-400 pin modules. The point has been reached where pin type connections are no longer adequate. There is a physical limitation on the number of pins which can be placed in a given area since each pin must be sufficiently large to withstand the normal insertion force. While low insertion force connection schemes have been devised they generally require more space and costly assembly devices. Even where pins are adequately sized to handle normal insertion forces a slight misalignment can easily result in a bent pin which leads to a scrap module. With simpler devices a modest number of scrap modules due to pin damage could be tolerated since the unit cost was not excessive. In the case of a large module with many circuits the cost has reached the point where module loss due to pin damage is no longer acceptable.
Another problem with pin connection arises during the module manufacturing process. The thermal mismatch between ceramic substrates and epoxy glass cards causes cracks during the step in which the module is soldered into the card. In addition, the brazing process is difficult to control and the fall out from this step is relatively high. Since the modules are virtually complete at the point when pins are brazed any scrap is very expensive. An alternative process with high yields and little scrap is very desirable.
The increased density of semiconductor modules and the resulting need for a greater number of connection pins has also led to the need for cable type connectors with greater numbers of pins and smaller size. Although the problems are similar, they are not identical and the differences have prevented the ready transfer of existing plug connection systems to semiconductor modules. As an example, a semiconductor module commonly dissipates so much heat that the design must provide for effective heat dissipation. Further, the semiconductor module desirably carries more connection points than the usual connector.
On the other hand, semiconductor modules have not usually required the ease of insertion which connectors must have. This aspect is now changing. Circuit density on semiconductor modules has reached the point where replacement of a defective pluggable card carrying multiple permanently mounted modules is not economically feasible. The defective module alone must be replaced. Generally this replacement is performed in a field environment which rules out the use of elaborate jigs or tools for this task.
The point has therefore been reached where there is a need for a high density connection system which has the characteristics of an easily used connector but which nevertheless accommodates all the particular requirements of a semiconductor package such as a large number of connection points and the ability to effectively dissipate heat.